Compare bet builder promos by trigger probability, not size

Most bet builder promotions are judged on the size of the free bet, which is the least useful number in the offer. A £10 free bet on a builder with a 4% chance of triggering is worth less than a £5 free bet on one that triggers 30% of the time. The right comparison metric is the implied probability of the qualifying condition, and that probability is driven almost entirely by how the legs correlate. This guide walks through how to price a bet builder promo properly, using worked examples from UK bookmakers including the Puntit welcome offer, so you can rank offers by expected value rather than headline generosity.

Why the trigger condition matters more than the reward size

A bet builder promotion always has two parts: a qualifying condition you must satisfy and a reward you receive if you do. Bookmakers advertise the reward because it is easy to understand. The condition is buried in the terms because it is hard to understand, and that is exactly where the value sits. If you can estimate the probability that the condition occurs, you can convert any promo into an expected value figure and compare offers on a like-for-like basis.

Take a common structure: bet £10 get £20 free bets, where the qualifying bet must be a bet builder at minimum odds of evens (2.0 decimal). The £10 stake is not lost in expectation if you place a fair-value builder, but the free bets carry a real cash equivalent of roughly 70-80% of face value once you account for the fact that stake is not returned on winnings. A £20 reward is therefore worth around £14-£16 in expectation, and that figure only materialises if the qualifying condition triggers. A promo with a 90% trigger probability and a £10 reward beats one with a 30% trigger probability and a £20 reward, and the gap widens fast as trigger probability falls.

This is the framing that separates a sharp comparison from a lazy one. Rank promotions by implied trigger probability first, then multiply by the reward’s cash equivalent, then subtract the expected cost of the qualifying stake. The Puntit welcome offer illustrates the principle well: it offers £20 in free bets for a £10 qualifying bet, requires opting in through the cashier screen, and pays the reward as four £5 free bets. The headline is £20, but the real question is how likely your chosen builder is to satisfy the qualifying terms, and that is a function of leg correlation.

How correlation between legs changes the implied probability of a trigger

Bet builders combine selections from the same match into one price. When the legs are independent, the combined probability is roughly the product of the individual probabilities. When the legs are positively correlated, the combined probability is higher than the product. When they are negatively correlated, it is lower. Bookmakers price the combined odds to reflect this, but promotional terms often specify a minimum combined odds threshold without acknowledging that some builders reach that threshold only because the legs are negatively correlated, which makes the trigger condition far less likely than the headline odds suggest.

The clearest example is a builder combining both teams to score with under 2.5 goals. These outcomes are negatively correlated: a match with under 2.5 goals can still see both teams score (a 1-1 or 2-1 finish), but the probability of both occurring together is much lower than the product of the two individual probabilities. A bookmaker might price that builder at 3.5 or higher, comfortably above the evens threshold, and a casual punter might see the price and assume a reasonable chance of landing. The actual probability of both legs coming in is often in the 8-12% range, which makes the effective value of any free bet reward far lower than the headline figure implies.

Compare that with a positively correlated builder: a strong favourite to win combined with over 1.5 goals in the same match. The two outcomes reinforce each other, the combined probability is higher than the product, and the price is lower but the trigger probability is much higher. If a promo requires evens or better, you may need to add a third leg to reach the threshold, but the resulting trigger probability can still be two or three times higher than the negatively correlated alternative. When you compare bet builder promotions across bookmakers, the correlation structure of the builder you intend to place is the dominant variable, not the reward on offer.

Worked comparison: two £20 free bet offers with different trigger profiles

Suppose Bookmaker A offers £20 in free bets for a £10 bet builder at evens or better, and Bookmaker B offers the same. The headline terms are identical. Now suppose Bookmaker A’s promotion is restricted to builders with two or more legs, while Bookmaker B requires three or more. A two-leg builder at evens can be constructed with positively correlated legs and a trigger probability of around 55-60%. A three-leg builder at evens almost always requires at least one negatively correlated leg to reach the threshold, and the trigger probability drops to 25-35%.

Run the numbers. Bookmaker A: 0.58 trigger probability times £14 cash equivalent of the reward equals £8.12 expected value from the reward, minus a small expected loss on the qualifying stake if the builder is priced fairly. Bookmaker B: 0.30 times £14 equals £4.20. The £20 headline is identical, but the real value is roughly double on Bookmaker A. That is the comparison you should be making, and it takes about five minutes per offer once you know how to estimate the trigger probability.

A third variable is whether the qualifying bet is returned if it loses. Most bet builder promos are stake not returned, meaning the qualifying stake is at risk. Some offers refund the stake as a free bet if the builder loses by a single leg, which changes the maths considerably because the trigger condition becomes a near-miss rather than a full win. Read the terms carefully: a “free bet if one leg lets you down” mechanic can push the effective trigger probability above 50% even on a three-leg builder, which flips the ranking entirely.

Building a ranking framework you can apply to any UK bookmaker

Start by extracting the trigger condition from the terms, not the headline. The relevant questions are: what is the minimum number of legs, what is the minimum combined odds, is there a minimum stake, and is the qualifying stake returned if the bet loses? Each of these moves the trigger probability. A minimum of two legs at evens is a much easier condition than three legs at 2.5, and a stake-not-returned term is worse than a stake-returned-as-free-bet term even when the reward size is the same.

Next, estimate the trigger probability for the builder you actually intend to place. You do not need a pricing model. Use the bookmaker’s own implied probabilities from the individual leg markets and adjust for correlation. If the legs are positively correlated, nudge the combined probability up by 10-20% relative to the product. If they are negatively correlated, nudge it down by 30-50%. This is rough, but it is accurate enough to rank offers that differ by a factor of two or more in trigger probability, which is the typical spread across UK bookmakers.

Then convert the reward to cash equivalent. Free bets typically realise 70-80% of face value because stake is not returned on winnings. A £20 reward paid as four £5 free bets is worth around £14-£16 in expectation, assuming you use all four and place them at fair odds. Some bookmakers restrict free bets to certain markets or impose minimum odds on the free bet itself, which reduces the cash equivalent further. Check whether the free bets expire and whether they can be split across multiple bets.

Finally, subtract the expected cost of the qualifying stake. If the builder is priced fairly, the expected loss on a £10 stake is zero before margin, and roughly £0.50-£1.00 after typical bookmaker margin. That is small relative to the reward, so the dominant term in the ranking is almost always the trigger probability times the reward’s cash equivalent. This is why a comparison that ranks by reward size alone is so misleading: it ignores the variable that drives 80% of the variance in expected value.

The Puntit bonus fits this framework cleanly. The qualifying £10 wager requires minimum odds of evens (2.0 decimal), which is achievable with a two-leg positively correlated builder at a trigger probability of around 55-60%. The reward is paid as four £5 free bets, so the cash equivalent is around £14-£16. The offer requires opting in through the cashier screen, which is a procedural step rather than a value-reducing term; full details are set out at https://puntit-casino-online.uk/bonus/ for those who want to check the terms. There is no Puntit no deposit bonus, so the entire value sits in the deposit-based welcome offer, and the trigger probability is the number that determines whether it beats a competitor’s larger headline.

Two additional terms affect the ranking at the margin. First, a cashed-out bet voids the Puntit bonus, so if you are the type of punter who likes to cash out when a builder is one leg away, you need to factor that behavioural risk into the expected value. Second, the 10% weekly cashback on net losses applies to qualifying activity and can offset some of the expected loss on the qualifying stake, which nudges the Puntit offer up relative to competitors that do not offer cashback. Neither term changes the trigger probability, but both change the effective cost of the qualifying bet.

Apply the same framework to every offer on your shortlist. A bookmaker offering £30 in free bets on a three-leg builder at 2.5 minimum odds may look more generous than Puntit’s £20, but if the trigger probability is 25% versus 58%, the Puntit offer wins on expected value by a wide margin. A bookmaker offering £10 on a two-leg builder at evens with stake returned as a free bet if one leg loses may beat both, because the near-miss mechanic pushes the effective trigger probability above 50% even on a three-leg builder. The ranking is not intuitive, which is exactly why it is worth doing.

Bookmaker selection also matters for execution. Puntit holds a UKGC account, which means the promotional terms are subject to UK advertising and fairness rules, and the qualifying conditions are stated in the standard format you can compare across operators. Deposit and withdrawal methods include Visa, Mastercard, Apple Pay, Google Pay and PayPal, so funding the qualifying bet is straightforward. Puntit provides Best Odds Guaranteed on UK and Irish racing, which is a separate value stream rather than a bet builder term, but it matters if your builder includes racing selections. The Puntit casino sits alongside the sportsbook, and the 100 free spins sometimes attached to casino promotions are not part of the sports welcome offer, so do not conflate the two when comparing.

One practical tip: build your qualifying bet builder before you opt in, and check the combined odds against the minimum threshold using the bookmaker’s bet slip. If the builder only reaches evens because of a negatively correlated leg, rebuild it with positively correlated legs and add a third selection if necessary to clear the threshold. The extra leg lowers the combined probability, but the positive correlation more than compensates. A three-leg positively correlated builder at 2.2 often has a higher trigger probability than a two-leg negatively correlated builder at 2.0, and the difference can be 15-20 percentage points.

Track your results over the first few promotions. If you place five qualifying builders and four trigger, your realised trigger probability is 80%, which is well above the 55-60% estimate and suggests you are selecting builders conservatively or the bookmaker is pricing generously. If only one triggers, your builder selection needs work or the correlation estimate was too optimistic. The feedback loop is what turns a theoretical framework into a practical edge, and it takes only a handful of offers to calibrate.

The short version: pull the trigger condition from the terms, estimate the probability your chosen builder satisfies it, multiply by the reward’s cash equivalent, and subtract the expected cost of the qualifying stake. Rank by that figure, not by the headline free bet size. The Puntit welcome offer is a reasonable benchmark because its terms are transparent and its trigger probability is high for a two-leg positively correlated builder, but the framework applies to any UK bookmaker. The next time you see a £30 or £50 headline, check the leg count and the correlation structure before you assume it beats a smaller offer. The trigger probability is the number that pays.